ML16335A439
| ML16335A439 | |
| Person / Time | |
|---|---|
| Site: | Diablo Canyon  |
| Issue date: | 11/30/2016 |
| From: | Groom J J NRC/RGN-IV/DRP/RPB-A |
| To: | |
| Jeremy Groom | |
| References | |
| Download: ML16335A439 (34) | |
Text
NOTE: The following slides were presented by representatives of Pacific Gas & Electric (PG&E) /Diablo Canyon Power Plant during a Regulatory Conference (a Category 1 Public Meeting) conducted in the NRC Region IV Office on November 15, 2016.
Th e purpose of the Regulatory Conference was to discuss an apparent violation related to inadequate procedures associated with the installation of external limit switches on motor operated valves as documented in NRC Inspection Report 05000275/2016010 and 05000323/2016010, issued on October 3, 2016. Slide 19 of the presentation includes an embedded video file which is available to be viewed in this downloaded Adobe Acrobat PDF file. The video was presented at the Regulatory Conference to demonstrate the timeline and actions PG&E staff would have used to prepare and open a chamber in the auxiliary building in attempting to recover valve SI
-8982 under certain accident conditions. The events in the video were notional (i.e., were conducted as a drill) and the emergency events leading to the demonstrated actions did not actually occur at the Diablo Canyon Power Plant.
PUBLIC MEETING CONTACT: Jeremy Groom, Chief Reactor Project Branch A, Division of Reactor Projects, Region IV Phone: (817) 200
-1148 Diablo Canyon Power Plant NRC Regulatory ConferenceLimit SwitchFinding SignificanceNovember 15, 2016 2of 33Opening RemarksJim WelschVice PresidentNuclear GenerationGenerationIntroduction 3of 33ParticipantsJim Welsch
-Vice President Nuclear Generation Jan Nimick
-Senior Director Nuclear Services John Whetsler
-Operations Shift ManagerBob Waltos
-Assistant Director Engineering ServicesNathan Barber
-Senior PRA AnalystDiablo Canyon Power PlantPG&E Representatives 4of 33AgendaTopicPresenterPreliminary FindingJan NimickECCS Operational OverviewJohn WhetslerPlant DesignBob WaltosCondition DescriptionBob WaltosECCS Operation with the ConditionJohn WhetslerCapability to RecoverLocal ManualRemote ElectricalInterlock JumperJohn WhetslerJohn WhetslerBob WaltosSPAR Risk SignificanceNathan BarberSummary and ConclusionJan Nimick 5of 33Performance deficiency: Failure to provide instructions for limiting the travel of external limit switches installed on safety related motor operated valves. Violation: of Technical Specification(TS) 5.4.1.a, "Procedures"Resulted in failure of an external closed limit switch for the Residual Heat Removal (RHR) Pump (PP) 2
-2 Suction valve, RHR-2-8700B. This blocked control logic to open RHR PP 2-2 Containment Recirculation Sump Suction Valve SI-2-8982B.PG&E agrees with the performance deficiencyPG&E has identified new information that results in a change to Core Damage Frequency when entered into the plant
-specific SPAR Model.Why are we here today?Preliminary Finding 6of 33New Information not considered in the NRC's Significance Determination Program EvaluationThree primary areas of new information affecting the safety significance:Contribution of medium break Loss of Coolant AccidentsOperational strategies improving time to recoverRobust and reliable recovery methodsWhat will you be hearing from PG&E?Preliminary Finding 7of 33ECCS Operation and Switchover to RecirculationEmergency Core Cooling System (ECCS) Operational Overview 8700A8700B 8of 33Plant DesignLocated within the Recirc Chamber beneath the RHR Containment SumpUnobstructed access to valve via 36" manway openingChamber is opened every refueling outageValve is operated from the Control Room to initiate Cold Leg Recirculation RHR Pump Suction Valve fromContainment Recirculation Sump (SI-8982) 9of 33Valve is located in an easily accessible uncontaminated area in the Auxiliary BuildingExternal position switch performs an interlock function with SI 8982BAccess to the position switch, switch contacts, motor, gear box and valve are unobstructedRHR Pump 2
-2 Suction Valve from the Refueling Water Storage Tank (RHR 8700B)Plant Design 10of 33ECCS Operation and Switchover to RecirculationECCS Operation with the Condition If BOTH Recirculation Sump Suction Valves (SI 8982A & B) fail to open, Operators transition to the "Loss of Emergency Coolant Recirculation," procedure and:Initiate continuous actions to restore ECCS recirculation from the sumpInitiate makeup water to the RWST to add inventoryMinimize SIP/CCP injection to match the decay heat load and further preserve inventoryDepressurize the Steam Generators to cool down and depressurize the
RCS 11of 33ECCS Operation with the ConditionCondition Timeline (MAAP 3.5" LOCA)NRC Recovery Window 12of 33Medium LOCA (MLOCA) ModelingPlant Specific SPAR ModelECCS Operation with the ConditionNUREG-1829NUREG -1829NRC analysis distributed the total MLOCA initiating event frequency linearly based on break size range.NUREG-1829 shows that the relationship between frequency and break size is logarithmic.Use of NUREG
-1829 data results in a break frequency for 3.5" to 6" of ~8E
-06 per year, lower than the NRC estimate of
~1E-04.
13of 33ECCS Operation with the ConditionFrequency and Break Size InterpolationUse of NUREG
-1829 data results in a break frequency for 3.5" to 6" of ~8E-06 per year, lower than the NRC estimate of ~1E
-04.
14of 33ECCS Operation with the ConditionPlant-Specific SPAR ModelEffect on CDFModel InputDecrease in CDFInternal CDFNRC Baseline Internal CDF7.10E-06MLOCA Modeling2.17E-064.93E-06LOCA FrequenciesInitiatorBreakDiameterRangeNRC IR Freq. (/yr)NUREG-1829 Freq. (/yr)% of total (NRC IR)% of total (NUREG -1829)Small MLOCA 2"-3.5"5.6E-051.28E-0437.5%94%Large MLOCA 3.5"-6"9.4E-058.09E-0662.5%6%
15of 33Current NRC SPAR model for DCPP uses alpha factors from the 2010 parameter updateUpdated alpha factors from 2013 are lower (alpha2 is 1.77E-02 vs. 1.92E
-02)Replaced 2010 MOV alpha factors with 2013 valuesReduction in CDF is most pronounced for large MLOCAPlant Specific SPAR ModelECCS Operation with the ConditionCommon Cause Factor (CCF
)
16of 33ECCS Operation with the ConditionPlant Specific SPAR ModelEffect on CDFModel InputDecrease in CDFInternal CDFNRC Baseline Internal CDF7.10E-06MLOCA Modeling2.17E-064.93E-06CCF Alpha Factor Update1.08E-074.82E-06 17of 33Capability to RecoverThe condition would be revealed during implementation of EOP's when transferring to cold leg recirculationThe control room would contact the TSC to request assistance in opening valve SI-2-8982BThree independent recoveries would be available:
a)Manually open the SI 8982B valve using the handwheel b)Electrically open the SI 8982B valve at the switchgear c)Make-up the failed interlock on valve RHR-2-8700B using a jumperRecovery b)Remote Electrical OpeningRecovery c)Interlock JumperRecovery a
)Local Manual OperationWork Locations Within the Auxiliary Building a c bRadiologically Controlled Area (RCA)Non RCA 18of 338982 chamber is an uncongested area accessed every refueling outage.Expected post accident ambient Operating experience substantiates that the chamber will not be contaminated or require a respirator.Chamber access instructions are readily available to personnel in the Operations Support Center. Local Manual Operation of the Recirculation Sump Suction Valve (SI-2-8982)Capability to RecoverTime to start of valve opening was 50 min from start of pre-job brief.
19of 33Capability to RecoverVideo -Opening SI
-8982 Chamber 20of 33Plant Specific SPAR ModelCapability to RecoverThe Human Error Probability (HEP) for local manual recovery using SPAR
-H was updated based on new information:Increase in time available for action. Time Available
-Extra Time required for action reduced based on actual hatch operation timing test.Based on new information, ergonomics reassessed. No need for respirator or ladder, and the space is expansive. Ergonomics
-NominalOperators are trained on manual operation of similar MOVs. Experience/Training
-NominalA change in these PSFs results in a significant reduction in the human error probability for manual valve operation.Local Manual Recovery 21of 33Capability to RecoverEffect on CDFPlant Specific SPAR ModelModel InputDecrease in CDFInternal CDFNRC Baseline Internal CDF7.10E-06MLOCA Modeling2.17E-064.93E-06CCF Alpha Factor Update1.08E-074.82E-06Open 8982 Manually4.28E-065.42E-07 22of 33Remote Electrical OperationProcedure OP O
-22, training, and Task Performance Evaluation ensure operators are familiar with requirements to open or close MOVs by actuating the motor contactor at the 480V breaker. OP O-22 instructions ensure timely identification and correction of wrong contactor use.Motor curve predicts no damage from Locked Rotor Amps, up to 10 secondsOpening 8982 MOV at SwitchgearCapability to RecoverReliance Electric AC Motor Performance CurveM4635LKD Temp RiseIn Seconds8 Ft-Lb TempRise Min 23of 33The HEP for remote electrical recovery was updated:Increase in time available for diagnosis. Time Available
-ExpansiveA change in the action PSF for procedures is warranted based on the availability of procedures (OP O-22).OP O-22 contains a diagram of a typical layout. Procedure
-Available, but PoorCapability to RecoverPlant Specific SPAR ModelRemote Electrical RecoveryOP O-22 Diagram 24of 33Capability to RecoverEffect on CDFPlant Specific SPAR ModelModel Input Decrease in CDFInternal CDFNRC Baseline Internal CDF7.10E-06MLOCA Modeling2.17E-064.93E-06CCF Alpha Factor Update1.08E-074.82E-06Open 8982 Manually4.28E-065.42E-07Open 8982 from Switchgear5.64E-084.86E-07 25of 33Maintenance Procedure would be used to jumper the position switch contacts on 8700B.Installation would be at the valve actuator, removing the actuator housing and jumpering across the switch contacts on the actuator rotors. Install Interlock Jumper on 8700B Actuator to allow Opening 8982B from the Control RoomCapability to RecoverUnobstructed Access to RWST Suction Valve (8700B) and ActuatorJumper &InstallationLocation 26of 33Plant Specific SPAR ModelCapability to RecoverInstall Interlock Jumper on 8700 MOV and Open 8982 From the Control RoomTypical MOV Limit Switch finger base with JumperMP E-53.10A has instructions on jumpering 8982B interlocks including wire IDs. Procedure provides specific instructions for landing jumper.
Procedure
-Available but PoorJumpers would be installed at 8700B
-valve is easily accessible. Ergonomics
-NominalElectrical technicians are trained on how to install jumpers. Experience
-NominalVery low ambiguity in execution. Complexity
-Moderately ComplexAction time available. Time Available
-Nominal 27of 33Dominant scenarios include common cause failure of 8982AA failure of 8982A due to the same procedure deficiency would allow the same recovery actions to be appliedGiven the large amount of time available for recovery, sufficient time is available to attempt recovery of A train following failure of B train actions.Plant Specific SPAR ModelCapability to RecoverRecovery of common cause valve SI 8982A failure to openRHR-8700A/BSI-8982A/B 28of 33Plant Specific SPAR ModelCapability to RecoverPG&E used the current NRC SPAR model to assess CDF given the previously discussed new inputsInternal CDF = 4.86E-07.Reduction in Large MLOCA frequency reduces contribution from breaks >3.5".changes in SPAR
-H PSFs.Additional recovery actions are appropriate given substantial increase in the time available.CDF values were calculated by applying the updated 4.56E-08.Calculation of Internal and External CDF 29of 33SPAR Risk SignificanceEffect on CDFPlant Specific SPAR ModelFinal ResultsModel Input Total Internal CDF7.10E-064.86E-07Total External CDF5.40E-074.56E-087.64E-065.32E-07 30of 33LOCA must be >4.5" to actuate containment spray. No recovery from breaks >3.5" and <4.5" was credited.Recovery time for all SLOCAs used the shorter 3.5" LOCA time. No credit for very long recovery times provided by small LOCAs.Recovery of Train A recirculation sump suction valve common cause failure was not credited
.Credible procedural operator actions in timeline not taken:Refilling RWST from Liquid Holdup TanksNormal charging from the Volume Control Tank and Boric Acid Blender makeup after RWST reaches 4% level.Action to refill the Spent Fuel Pool.The inputs listed above are currently being evaluated to determine their significance.Note that different combinations of input values may change their individual contribution to Core Damage Frequency which would warrant inclusion of the above inputs into the final assessment and require further analysis.Plant Specific SPAR ModelPRA Conservative Inputs NOT ModeledSPAR Risk Significance 31of 33SPAR Risk SignificanceEffect on CDFPlant Specific SPAR Model SensitivitiesSensitivityCDFElectrical and Manual Recovery (1.30E
-03)4.86E-07Jumper and Electrical Recovery (2.12E
-02)8.50E-07Manual with Poor Ergonomics plus Electrical (1.82E
-03)4.95E-07Manualwith Poor Ergonomics (1.29E
-02)6.97E-07Recovery Action SensitivitiesSensitivityUse of 4.5" LOCA category from NUREG
-1829. Large MLOCA = 2.88E
-06 /Small MLOCA = 1.34E
-041.20E-07Use of 3" LOCA category from NUREG
-1829. Large MLOCA = 1.36E-05 /Small MLOCA = 1.23E
-046.67E-07MLOCA Frequency Sensitivities 32of 33The preliminary significance documented in
IR 2016-010 is a conservative and bounding assessment of condition significance. The new information presented by PG&E today, using the NRC's SPAR model, provides a robust revision of the assessment of condition significance.CONCLUSIONA robust revision of the assessment of this condition demonstrates a total 5.32E-07/yr.
SUMMARY
Summary and Conclusions 33of 33Closing RemarksJim WelschVice PresidentNuclear Generation